Dynamic viscosity, also known as absolute viscosity, measures a fluid's internal resistance to flow when subjected to an external force. In engineering, two common units used to quantify this property are the Centipoise (cP) and the Pound per foot-second (lb/(ft·s)).
Centipoise (cP): A CGS (centimeter-gram-second) unit commonly used in industrial chemistry and fluid mechanics. It is defined as one-hundredth of a Poise. Water at 20°C has a viscosity of approximately 1 cP.
Pound per foot-second (lb/(ft·s)): A unit derived from the English Engineering system. It is frequently utilized in legacy mechanical engineering specifications and thermal-hydraulic calculations in the United States.
The relationship between these units is defined by the conversion factor \(1 \text{ cP} \approx 0.00067197 \text{ lb/(ft·s)}\). Understanding this conversion is critical when transitioning between metric-based laboratory data and imperial-based design standards.
Centipoise to Pound per foot-second Conversion Reference Table
Centipoise (cP)
Pound per foot-second (lb/(ft·s))
0.1
6.7197e-05
0.5
3.3598e-04
1.0
6.7197e-04
2.0
0.0013
5.0
0.0034
10.0
0.0067
20.0
0.0134
50.0
0.0336
100.0
0.0672
500.0
0.336
1000.0
0.672
Conversion Example: 10 cP to lb/(ft·s)
To convert a dynamic viscosity value from Centipoise to lb/(ft·s), multiply the value by the conversion factor of 0.0006719689496587741.
The conversion factor is small because the Pound per foot-second is a significantly larger unit of dynamic viscosity compared to the Centipoise. One lb/(ft·s) is equivalent to approximately 1488.16 cP.
No, the SI unit for dynamic viscosity is the Pascal-second (Pa·s). While cP is widely accepted in industry, it is technically a CGS unit, and lb/(ft·s) belongs to the Imperial/US Customary system.
"On fait la science avec des faits, comme on fait une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison." "Science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house." — Henri Poincaré (French Mathematician, Theoretical Physicist & Mining Engineer)